Las Vegas police have asked football superstar Cristiano Ronaldo to submit a DNA sample as part of their investigation into rape allegations made against him.

The police want to see if Ronaldo's DNA matches that found on the dress of the woman who accused him of rape, the Wall Street Journal reported, adding that the police have issued a warrant to acquire the DNA.

The Juventus forward has vehemently denied the accusations ─ with his lawyer, Peter Christiansen, telling AFP the request was standard procedure.

"Mr Ronaldo has always maintained, as he does today, that what occurred in Las Vegas in 2009 was consensual in nature, so it is not surprising that DNA would be present, nor that the police would make this very standard request as part of their investigation," he said in a statement.

The Las Vegas Metropolitan Police Department said it had made an official request to Italian authorities, adding it is "taking the same steps in this case as in any other sexual assault to facilitate the collection of DNA evidence."

Former model Kathryn Mayorga, 34, of Las Vegas, accused Ronaldo in a complaint filed last year in the state of Nevada.

She claims after meeting him at a Las Vegas nightclub, he raped her at his hotel suite on June 13, 2009 ─ just before he joined Real Madrid from Manchester United. Mayorga alleges she was paid $375,000 to keep quiet.

Ronaldo's lawyers have said that the non-disclosure agreement signed with the former model is "by no means a confession of guilt".

Mayorga's attorney has previously said that the model agreed to an out-of-court settlement to keep her name from going public, but was inspired to speak out by the #MeToo movement against sexual harassment.

Mayorga's attorney could not immediately be reached for comment on Thursday.